Foamed plastic paddle or vane



Dec. 22, 1970 c, RQPER 3,548,52fi

FOAMED PLASTIC PADDLE OR VANE Filed Oct. 2. 19s? INVENTOR.

EDWARD CULLUM ROPER V 1 W/ZL1W% ATTORNEY United States Patent l3,548,522 FOAMED PLASTIC PADDLE 0R VANE Edward Cullum Roper, Stamford,Conn, assignor to American Machine & Foundry Company, a corporation ofNew Jersey Filed Oct. 2, 1967, Ser. No. 672,331 Int. Cl. B32!) 3/26,5/18; E01h 5/00 US. Cl. 37-43 5 Claims ABSTRACT OF THE DISCLGSURE Apaddle or vane having a substantially unfoamed outer skin and a foamedinner core made by molding from a polyethylene having particularproperties.

This invention relates to structural paddles or vanes. Moreparticularly, the invention relates to structural paddles or vanescomprising high impact resistant, foamed polyethylene and suitable foruse on snow removing apparatus, such as a snow blower, although suchpaddles or vanes can be used on other devices or for other suitablepurposes depending upon the particular shape in which they areconstructed. However, for the sake of simplicity the invention will bedisclosed as it relates to paddles or vanes suitable for use on snowremoving machines.

Presently most snow removing apparatus, such as snow blowers arenormally equipped with single or multiple impeller vanes or paddles.Such paddles or vanes commonly react against the force provided by theinertia of the snow which is being removed. Consequently, these vanes orpaddles are subjected to constant flexural stresses and at times toextremely high flexural impact shocks when they come into contact withice patches, hidden boulders, logs or other like obstructions. As aresult of the stresses to which such paddles or vanes are subjected,they have generally been constructed of tough metals, such as steeland/or alloys thereof, aluminum and/or alloys thereof and the like.However, when constructed of such metallic materials in order to obtaingood strength and high impact resistance, the vanes or paddles must bemade of relatively heavy gauge material which creates problems ofexcessive bulk and excessive weight, especially when they are to be usedon snow blowing apparatus operated by an individual and normally used inclearing driveways, walkways, steps, porches and the like around privateresidences.

Attempts to construct suitable metallic paddles or vanes from lightergauge materials such as aluminum, for example, on the other hand, resultin low impact resistance and low strength. Consequently, they are easilybent or distorted from their original shape when subjected to normalusage. This is so even though the light weight material is satisfactoryfrom a viewpoint of weight in utilization in the smaller type of snowblowing device used around private residences. Accordingly, there existsa need for the provision of impeller paddles or vanes, regardless ofshape, suitable for such snow blowing apparatus as mentioned hereinaboveand which paddles combine the lightness in weight of the light gaugemetal vanes and paddles and the structural strength of the heavy gaugemetal paddles and vanes.

The present invention fulfills this need by providing a snow blowerpaddle or vane having a substantially unfoamed outer skin aiid a foamedinner core made by molding from a polyethylene having particularproperties.

In order to understand the present invention more fully, reference ismade to the following description which is to be taken in conjunctionwith the accompanying drawing wherein:

FIG. 1 is a view in perspective of a snow blower 3,548,522 Patented Dec.22, 1970 paddle or vane made in accordance with the invention;

FIG. 2 is an end view of the snow blower paddle of FIG. 1, and

FIG. 3 is a view in section taken along line 1--1 of PEG. 1 showing thefoamed core and unfoamed outer s 1n.

Referring more particularly to FIG. 1, the snow blower paddle or vaneillustrated there and generally designated by numeral 11 is molded froma linear polyethylene containing a foaming agent and having a bulkdensity of .75 gram per cubic centimeter based on a linear polyethylenehaving a specific gravity of .96, a weight average molecular weight ofabout 250,000, determined in any suitable known manner, and a melt index1 at approximately 190 C. in a range of about .14 to about .22 asdetermined by ASTM test method D-1238. Like paddles or vanes can also beconstructed from polyethylenes having a weight average molecular weightin excess of from about 250,000 up to about 8,000,000 or more, when suchmaterials are available and the melt indexes thereof do not exceed about.3. In contrast, polyethylenes having weight average molecular weightsof about 200,000 and below and specific gravities of below about .96 aswell as melt indexes of .3 and above do not result in structural paddlesor vanes having suitable properties with respect to strength whensubjected to flexural impact shocks.

The paddle illustrated in FIG. 1 has the shape of a compound curve. Morespecifically, the illustrated paddle or vane 11 is molded so that it hasa substantially vertical lip 12 for attachment to an axial supportingmember (not shown) on a snow blowing apparatus. The vertical lip 12 isprovided with a plurality of slots 13 which cooperate with screws, boltsor like means on the axial supporting member mentioned above.

Extending in a substantially horizontal direction with respect to thelip 12 is the main body portion 14. Body portion 14 may also slopeslightly downwardly, if desired, as it extends horizontally and slopessharply downwardly toward each side as shown at 15. Thus, the leadingedge of the main body portion takes on a concave shape as shown at 16.Accordingly, the overall shape of paddle or vane 11 forms a scoop-likeconstruction which vastly improves the eificiency in snow removingoperations.

As shown more specifically in FIG. 3, the subject vane has a foamed coreand a substantially unfoamed outer skin designated by numerals 17 and18, respectively.

The density of the unfoarned outer layer or skin 18 is at least about1.5 times the density of the central area of the cellular core 12. Thedense outer layer generally may vary in thickness or depth from about 60to about mils at the surface of the paddle or vane. Moreover, thedensity of the paddle increases from the central area of the core outtowards the substantially unfoamed outer skin, giving a foam bulkdensity of about 40 to about 48 pounds per cubic foot in the finalproduct and a density in a range of from about 30 pounds per cubic footto about 38 pounds per cubic foot extending from the central core to thesubstantially unfoamed outer skin.

This particular type of foamed structure aids in providing the necessarystrength while at the same time permitting required flexibility and alsoresults in the distribution of force on impact with a solid article.

In contrast to like paddles or vanes made of steel and aluminum, paddlesof this invention molded from the particular polyethylene describedshowed unexpectedly high impact resistance even at low temperatures. Forexample, metal vanes made of 2" gauge aluminum were easily bent andbroken under the impact of a 10 pound weight dropped from a height ofabout 4 feet at temperatures of 20 C. and lower. Like paddles made of Agauge steel were also easily bent and broken under impact when subjectedto the same tests.

In contrast, the paddles or vanes of this invention, when subjected tothe same tests, did not bend or shatter. Vanes or paddles made of steelhaving comparable strength to the paddles of this invention were of /1gauge material and weighed twice as much as the subject paddles.

A paddle or vane in accordance with this invention can be prepared by asuitable molding process wherein the high molecular weight linearpolyethylene having a gas forming agent incorporated therein is eitherplaced directly in a heated mold and brought to thermoplastic state inthe mold or is rendered thermoplastic and then injected or fed into amold in any suitable fashion. In carrying out the practice of theinvention any thermally sensitive gas forming agent which liberates gasat the desirable temperature including solids, gases or liquid gasforming agents may be utilized. Suitable agents which can be employed toexpand the high molecular weight polyethylene include, for example,water, air, carbon dioxide, nitrogen, Freon, azodicarbonamide,p,p-oxy-bis- (benzene sulfonyl hydrazide), diazoaminobenzene,nitroguanidine, N,N-dinitrosopentamethylenetetramine, azobisformamide,azobisisobutyronitrile, N,N' dimethyl- N,N'-dinitrosoterephthalamide,benzene sulfonyl hydrazide, benzene-1,3-disulfonyl hydrazide,diphenylsulfon- 3,3'-disulfonyl hydrazide, 4,4'-oxy-bis-(benzenesulfonyl hydrazide), ammonia blowing agents, such as, urea, biuret,ammonium carbonate and the like, petroleum ether, butane, n-pentane,isopentane, neopentane, isobutane, hexane, heptane and the like, theperchlorofluorocarbons, such as, trichlorofluoromethane, symmetricaltetrachlorodifiuoromethane, 1,1,2-trichloro 1,2,2 trifluoroethane,symmetrical dichlorotetrafluoroethane, 1-chloro-1,1,2,2,2-pentafluoroethane, 1-chloro-1,2,3,3,4,4 hexafluorocyclobutane,1,2-dichloro-1,2,3,3,4,4 hexafluorocyclobutane and the like. Mixtures ofany two or more of the gas forming reagents can also be utilized. Amongthe agents mentioned above, however, azodicarbonamide is a preferred gasforming material.

The amount of gas forming agent utilized is dependent upon the extent towhich it is desired to expand the thermoplastic linear high molecularweight polyethylene. Generally, in order to obtain paddles or vaneshaving the desirable cellular structure and consequently the desireddensity requirements, only a relatively small amount of the gas formingagent is needed, generally about 0.25 percent by weight, based on theweight of the thermoplastic polymer, being at least sufiicient and up toas much as about 2.0 percent by weight. In a few instances the amount ofgas forming agent needed may be equal to or exceed 4 percent by weightof the thermoplastic polymer.

As mentioned hereinabove, the preparation of paddles or vanes inaccordance with this invention can be accomplished by any suitablemolding procedure. Howev r, one preferred procedure involves theextrusion of the thermoplastic polyethylene in a screw type injectionmolding apparatus under pressure at least sufficient to preventexpansion of the gas forming agent and at temperatures at leastsufficient to decompose the gas forming agent and melt the thermoplasticmaterial after which the plastic melt is injected at a lower pressure,preferably atmospheric, into a suitable mold. By this particular processthe normally solid thermoplastic polymer, generally having been premixedwith a sufiicient amount of solid gas forming material is fed to theextruder in the form of a flake or pellet. In the first section of thescrew as the resin is rotated, it tends to stick to the barrel as it ispushed forward by the flights on the screw. Plasticization begins atthat point when the resin particles start to adhere to each other, tothe screw and to the barrel. Heat from the barrel as well as from thefiuxing of the polymer particles by the screw contribute to theelevation of the temperature, making it sufficiently high to melt thepolymer. The term fiuxing as employed herein refers to the melting ofthe solid polymer particles so that they run together and coalesce witheach other and are likewise forced against the surfaces of the screw andthe barrel. This fluxing causes a deforming and shearing action and theheat caused thereby reduces the polymer to a molten state.

During this plasticizing process, the polyethylene goes through a phasechange from a solid to a viscous melt while at the same time acompacting phase takes place as the bulk density is increased and as thepressure builds up. While under compression the homogeneous mass isprevented from expanding. The plasticization can take place in both thefeed and transition or compression zones of the extruder. However, itshould be complete by the end of the transition zone at which time thepolymer should be in the form of a uniform melt.

The last section of the screw type extruder is the metering section inwhich the channel depth of the screw is at its smallest and is constantfor about four turns, thereby providing a measured amount of uniformpolymeric melt which is pumped out of the extruder barrel and into asuitable mold at a uniform rate. It is generally in this last section ofthe screw extruder that it is most advantageous to decompose the gasforming agent or in those instances where the agent is already in theform of a gas to add it to the polymeric melt.

The screw extruder is designed to provide sufficient time for heating ofthe polymer at each successive stage and also is designed withsufficient capacity in length to hold a number of charges. Accordingly,it is kept filled by metering the feed either by volume or by weight tobalance exactly the amount delivered into the mold.

The polymeric melt is then injected by axial reciprocation of the screwinto a suitable mold. The temperature of the mold is in excess of about60 C. preferably at about C. so that on molding of the material theexpanded gas formed by the gas forming agent is squeezed toward thecenter of the paddle or vane and leaves a well formed substantiallyunfoamed protective polyethylene layer around a cellular core. Paddlesor vanes so produced have excellent strength as mentioned hereinabove incomparison to those made from steel and aluminum. Moreover, such paddlesor vanes are remarkably light in weight and due to their strength have agreatly improved service life when compared to the life of metallicpaddles. Furthermore, the subject paddles and vanes have a good hardsmooth void-free outer layer. Such a surface reduces the sticking ofsnow to the surface of the paddle.

Numerous other advantages of this invention will be readily apparent tothose skilled in the art.

It will be apparent to those skilled in the art that variousmodifications of the invention may be made without departing from thespirit and scope thereof. Accordingly, the invention is not to belimited except as defined in the appended claims.

What is claimed is:

1. A scoop-like paddle having a substantially unfoamed outer skin and afoamed inner core, high impact strength and structural flexibilitymolded from a linear polyethylene foam having a bulk density ofapproximately .75 gram per cubic centimeter based on a linearpolyethylene having a specific gravity of about .96, a weight averagemolecular weight in excess of about 250,000 and a melt index 1 atapproximately C. in a range of about .14 to about .22, said paddlehaving a density which increases from the center of the core to amaximum at the substantially unfoamed outer skin, the main body portionof said paddle having the shape of a compound curve extendingsubstantially horizontally outwardly from a substantially vertical lipand sloping downwardly toward each side, the leading edge of said mainbody portion forming a concave shape.

2. A paddle as defined in claim 1 wherein the unfoamed outer skinextends inwardly to a depth in a range of 60 to 90 mils toward thecenter thereof.

3. A paddle as defined in claim 1 wherein the density is in a range ofabout pounds per cubic foot to about 38 pounds per cubic foot extendingfrom the central core to the substantially unfoamed outer skin.

4. A paddle as defined in claim 1 wherein the bulk foam density is in arange of about 40 to about 48 pounds per cubic foot.

5. A scoop-like snow blower paddle having a substantially unfoamed outerskin having a thickness of about to about mils, a foamed inner core,high impact strength and structural flexibility molded from a linearpolyethylene having a bulk density of approximately .75 gram per cubiccentimeter based on a linear polyethylene having a specific gravity ofabout .96, a weight average molecular weight of about 250,000, a meltindex I at approximately C. of about .2, a bulk foam density in a rangeof about 40 to about 48 pounds per cubic foot and a density in a rangeof about 30 pounds per cubic foot to about 38 pounds per cubic footextending from the central core to the substantially unfoarned outerskin,

the main body portion of said paddle having the shape of a compoundcurve extending substantially horizontally outwardly from asubstantially vertical lip and sloping downwardly toward each side, theleading edge of said main body portion forming a concave shape.

References Cited UNITED STATES PATENTS ROBERT F. BURNETT, PrimaryExaminer W. A. POWELL, Assistant Examiner US. Cl. X.R.

